CARDIOPULMONARY INTERACTIONS IN HEALTHY-CHILDREN AND CHILDREN AFTER SIMPLE CARDIAC-SURGERY - THE EFFECTS OF POSITIVE AND NEGATIVE-PRESSURE VENTILATION

Objective-To investigate the effects of cuirass negative pressure vent ilation on the cardiac output of a group of anaesthetised children aft er occlusion of an asymptomatic persistent arterial duct, and a group of paediatric patients in the early postoperative period following car diopulmonary bypass. Design-Prospective study. Setting-The paediatric intensive care unit and catheter laboratory of a tertiary care centre. Patients-16 mechanically ventilated children were studied: seven had undergone surgery for congenital heart disease, and nine cardiac cathe terisation for transcatheter occlusion of an isolated asymptomatic per sistent arterial duct. Interventions-Cardiac output was measured using the direct Fick method during intermittent positive pressure ventilat ion and again after a short period of negative pressure ventilation. I n five of the postoperative patients a third measurement was made foll owing reinstitution of positive pressure ventilation. Results-Negative pressure ventilation was delivered without complication, with no sign ificant change in systemic arterial oxygen and carbon dioxide tension. The mixed venous saturation increased from 74% to 75.8% in the health y children, and from 58.9% to 62.3% in the postoperative group. Negati ve pressure ventilation increased the cardiac index from 4.0 to 4.5 1/ min/m(2) in the healthy children, and from 2.8 to 3.5 1/min/m(2) in th e surgical group. The increase was significantly higher in the postope rative patients (28.1%) than the healthy children (10.8%). Conclusions -While offering similar ventilatory efficiency to positive pressure ve ntilation, cuirass negative pressure ventilation led to a modest impro vement in the cardiac output of healthy children, and to a greater inc rease in postoperative patients. There are important cardiopulmonary i nteractions in normal children and in children after cardiopulmonary b ypass, and by having beneficial effects on these interactions, negativ e pressure ventilation has haemodynamic advantages over conventional p ositive pressure ventilation.